This invention relates to a method of controlling injection of fuel supplied to an internal combustion engine having multi cylinders, and more particularly to a method of controlling simultaneous injection by fuel injection valves arranged for respective cylinders of the engine by means of a single time counter.
In an internal combustion engine provided with a plurality of cylinders and fuel injection valves corresponding to respective cylinders, in general, the amount of fuel supplied to the engine is controlled by adjusting fuel injection periods of time for which the fuel injection valves are energized or opened to inject fuel. The fuel injection periods of time for the fuel injection valves are measured by as many time counters which are provided for respective fuel injection valves. However, if the fuel injection periods of all the fuel injection valves can be measured by only one time counter, it would be possible to manufacture the fuel supply control system at low cost due to a lesser number of time counters.
When the engine is not in a particular operating condition such as a high speed condition and a high load condition, it would be possible to effect sequential injection through the respective fuel injection valves by sequentially measuring the respective fuel injection periods by the single time counter.
On the other hand, when the engine is in the particular operating condition, it is desirable to effect simultaneous injection through the fuel injection valves in order to secure a required fuel injection period of time and hence a desired fuel injection quantity.
In order to control such simultaneous fuel injection by means of a single time counter, a method is known e.g. from Japanese Provisional Patent Publication (Kokai) No. 49-45652, in which fuel injection valves are simultaneously controlled to open and close for simultaneous injection in accordance with a single fuel injection period signal common to all the fuel injection valves, supplied from a calculation circuit which corresponds to the time counter. Therefore, according to the known method, the fuel injection valves are opened and closed at the same time, whereby it is impossible to set different fuel injection periods for the respective fuel injection valves. However, the charging efficiency is different between the cylinders of the engine due to variations in air distribution characteristic in the intake air system, variations in tappet clearance between respective intake valves and exhaust valves, etc., and therefore there can occur variation in the air/fuel ratio of an air-fuel mixture supplied to the respective cylinders if the single fuel injection period is commonly set for all the cylinders according to the known method, resulting degraded emission characteristics, etc. This makes it difficult for a fuel injection system with a single time counter to find a practical use in spite of its low cost.